The Waldeyer ring equivalent in the rat. A model for analysis of oronasopharyngeal immune responses.

By means of serial sectioning of the head and neck a paired, rod shaped, parachoanic lymphoid organ was identified in Lewis rats. Histological, ultrastructural studies and FACS analysis showed this organ to be a lympho-epithelial organ with high endothelial venules (HEV) and a preponderance of B over T and T helper over T suppressor cells. Consequently this organ resembles the pharyngeal tonsil of man, and it is called the Waldeyer ring equivalent (WRE). The lymphatic drainage of this organ occurs predominantly to the deep, and to a lesser extent to the superficial cervical lymph nodes. Migration studies with 51Cr labeled cells show that the WRE lymphoid cells migrate into the lymphoid organs with HEV (peripheral lymph nodes. Peyer patches and WRE). In this respect they resemble peripheral lymph node cells more than cells from the Peyer patches. Thus the WRE lymphoid tissue in the rat is undoubtedly involved in local oronasopharyngeal immune surveillance and may also contribute to mucosal and systemic immune responses.

Immunohistochemistry of Nasopharyngeal (Waldeyer's ring equivalent) lymphoid tissue in the rat.

Previously we have described the presence of Waldeyer's ring equivalent (WRE) lymphoid tissue in the rat, and pointed out the importance of such an experimental model for studying the immunological role of nasopharyngeal lymphoid tissue. Here we extend this work with immunohistological data in terms of compartmentalization and distribution of the various lymphoid and non-lymphoid cells of this WRE lymphoid tissue in situ. WRE tissue consists of distinct T cell and B cell areas. B cell areas predominate; they are located directly under the mucosal epithelium and consist mainly of follicles. These follicles frequently contain a germinal center with IgD negative B cells interspersed with scattered CD4 (helper/inducer) T cells. Follicular dendritic cells are present in the germinal centers. T cell areas, on the other hand, are predominantly present at the abluminal side of the WRE in interfollicular areas. In these areas high endothelial venules and both CD4 and CD8 (suppressor/cytotoxic) T cell populations with a clear preponderance of CD4 over CD8 cells can be observed. MHC class II positive interdigitating dendritic cells are also scattered throughout these T cell areas. Mononuclear phagocytes (ED1-positive monocytes/macrophages) are scattered throughout the WRE, but especially in the T cell areas. A subpopulation of (ED3-positive) mononuclear phagocytes, e.g., the lymphoid tissue macrophage, is exclusively scattered between the small blood vessels along the abluminal side of the lymphoid tissue. Here, plasma cells, including those of the IgA type, are located. The data show that nasopharyngeal lymphoid tissue in the rat can be considered as an immunologically fully equipped and active mucosal lymphoid organ presumably executing similar immune functions as the tonsils in the human Waldeyer's ring.

Tonsillar (Waldyer's ring equivalent) lymphoid tissue in the rat: lymphocyte subset binding to high endothelial venules (HEV) and in situ distribution.

We have studied lymphocyte traffic to the Waldeyer's ring equivalent (WRE) lymphoid tissue of the rat, by measuring the in vitro binding of various lymphocyte subsets to high endothelial venules (HEV) in the WRE. In addition, we studied the in situ distribution of these lymphocyte subsets. WRE tissue consists of B and T cell areas; the latter contain HEV. B cells outnumber T cells, and T helper (CD4) cells outnumber T suppressor/cytotoxic (CD8) cells (T/B ratio = 0.7; CD4/CD8 ratio = 5.1). In vitro studies of lymphocyte binding showed that lymphocytes adhere almost equally well to HEV in WRE tissue as to HEV in lymph node (LN) tissue, and much better to HEV in WRE than to HEV in Peyer's patch (PP) tissue. T cells bind better than B cells to HEV in WRE (T/B binding ratio = 1.8), and CD8 cells better than CD4 cells (CD8/CD4 ratio of 2.9-3.2, dependent on cell source). The observed preference of T over B cells in binding to HEV is not reflecting the distribution of these lymphocyte sets in situ. In this respect the WRE takes a unique position, since in other lymphoid organs T/B binding ratios parallels T and B cell distribution in situ. This may suggest a much more rapid passage of T cells through the WRE than through other lymphoid tissues, although other mechanisms cannot be ruled out. The CD8/CD4 binding ratio to HEV in WRE contrasts with situ distribution of these cells also; however, this is found for LN and PP lymphoid tissue too.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of nasopharyngeal lymphoid tissue.

Nasal-associated lymphoid tissue (NALT), which comprises paired lymphoid organs in the nasopharynx of rodents, is the principal mucosal lymphoid tissue of the respiratory tract. As described in this review, NALT bears certain similarities to the Peyer's patches of the intestine but the two differ remarkably in morphology, lymphoid migration patterns and the binding properties of their high endothelial venules (HEV).